FIG. 1 is a side view showing a conventional rudder, in which a rudder stock is installed in a rudder stock trunk, and the position of the rudder stock secured to a rudder blade is set above the central line of a propeller shaft, FIG. 2 is a vertical sectional view taken along line II-II of FIG. 1, and FIG. 3 is a schematic view showing the placement of an inner bearing between the rudder stock and the rudder stock trunk according to the prior art, and the position of a coupling part of the rudder stock with the rudder blade.
In a balanced rudder for ships, as shown in FIGS. 1 to 3, part of a hull is denoted by reference numeral 110, a rudder stock trunk is denoted by reference numeral 120, a rudder blade is denoted by reference numeral 130, and a rudder stock is denoted by reference numeral 140. Further, reference numeral 220 denotes a propeller for propelling a ship, and a fin 135 is rotatably coupled to the rudder blade 130. Further, the rudder blade 130 functions to receive the lower end 120b of the rudder stock trunk 120, and preferably has a cylindrical cavity 160.
A central bore 125 is vertically formed in the cylindrical rudder stock trunk 120, which has the shape of a cantilever arm, and receives the rudder stock 140 therein. The rudder stock trunk 120 is secured at an inside end thereof to the hull 110, and extends into the rudder blade 130. The rudder blade is coupled to the end of the rudder stock 140. An inner bearing 150 is installed in the central bore 125, which is vertically formed in the rudder stock trunk, and supports the rudder stock 140 in the rudder stock trunk 120. Preferably, the bearing 150 is positioned in the lower end 120b of the rudder stock trunk 120. One end 145 of a lower portion 140b of the rudder stock 140 protrudes from the lower end of the rudder stock trunk 120 by a short distance. The tip 170 of the end 145 is coupled to the rudder blade 130. The coupling part of the rudder stock with the rudder blade has a general structure which allows the rudder blade 130 to be separated from the rudder stock 140 when a propeller shaft is replaced with another one. The coupling part of the rudder stock 140 with the rudder blade 130 is positioned above the central line 200 of the propeller shaft. Thereby, in order to disassemble the propeller shaft, a worker has only to remove the rudder blade 130 from the rudder stock 140.
That is, since the lower end 120b of the rudder stock trunk 120 and the lower portion 140b of the rudder stock 140 are positioned above the central line 200 of the propeller shaft, it is not necessary to remove the rudder stock 140 from the rudder stock trunk 120.
Further, the inner bearing 150 is installed in the rudder stock trunk 120 and supports the rudder stock 140. Preferably, the inner bearing 150 is placed in the lower end 120b of the rudder stock trunk.
Referring to FIG. 1, the fin 135, which is rotatably coupled to the rudder blade 130, is controllably rotated about a vertical axis line 135a by a general control driving unit. FIG. 3 schematically shows the position of the inner bearing 150, placed between the rudder stock 140 and the rudder stock trunk 120, and the position of the part of the tip 170 of the rudder stock that is coupled with the rudder blade relative to the central line 200 of the propeller shaft.
Such a balanced rudder for ships can be applied to all kinds of ships, including small ships and large ships. However, a structure for more efficiently stabilizing the bending moment of the rudder has been required. To this end, the problems of a construction including a vertical bearing must be overcome, and a structure for more efficiently stabilizing vibrations is required.